banania, I'm at the same point
As I've read methacrylate Polycarbonate is opaque to UV, but I would like to buy from a reputable source, I only have a pair of eyes.
Any recommendation reliable and not expensive, please?

Edit, corrected after Ch Krebs post_________________Pau

Last edited by Pau on Sat Feb 11, 2017 1:21 pm; edited 1 time in total

Stay away from GTL or anything that "claims" over 3500/4000maH. Samsung are another good choice. Also watch out for counterfeits, anything that costs less than $3/cell might be suspect. Please don't ask how I know

I am still waiting for torches, spectrometer etc. but in the mean time I was able to get the software for my old spectrometer. This spectrometer is too limited for reliable tests, but the qualitative results are indicative of what one should expect from a UV LED torch like the MTE 301, which uses a Nichia LED.

This is an uncalibrated spectrum of UVA and VIS indigo and blue regions. The sharp peak is the roughly 365 nm LED emission. The plateau at the right corresponds to blue, and might be the result of lint fluorescence on the window of the torch (there is plenty). This torch is equipped with a U340 window that cuts all VIS emitted by the LED, so we are not seeing the results of a LED "leak". I don't know what the small spikes come from, but I suspect they are artefacts of the spectrometer. They are not random noise because this spectrum is averaged from 10 readings, and the spikes are visible in each reading.

Meanwhile a fast question: do any plastic goggles/sunglasses or actually anything plastic shield enough from 365 nm UV -light or is there a need for some sort of dedicated UV protectors?

Polycarbonate is what is often used in "clear" protective glasses. It really cuts off wavelength shorter than 400nm. That said, be sure to purchase goggles/glasses that specifically state the they block "99.9%" UV. (And naturally if you are into welding, lasers or some really exotic lights then you need to do some research to get the proper eye-wear. ANSI Z87.1 is a rating that most all safety google/glasses should meet. See: http://blog.safetyglassesusa.com/what-does-ansi-z87-1-2010-certified-mean/ )

Thanks Charles. Actually now that I checked I found 3 different safetyglasses but only one of them had this Z87 marking. Those were also fairly expensive (close to 20 euros). The other two were cheaper (a couple of euros) and claim to have have some kind of UV-protection, but no Z87 marking on them.

I asked about plastic eye protection in general because I asked that question a couple of years ago from a sales person supplying UV gear and was given the advice that all protective plastic goggles should do the job. I wasn't sure if the advice was good and purchased my Z87 polycarbs anyhow. Maybe he meant that all clear safetyglasses are (here in Finland) made of polycarb, I don't recall the exact wordings.

A layer of polycarbonate (Lexan) is used in diamond color analysis to block UV that may excite fluorescence in the diamond , which can affect its' color grade. This is when fluorescent lighting is used. All fluorescent lights leak UV particular from the 365nm mercury line which is a very strong peak. White LEDs are also fluorescent most of the time but the excitation is usually 405 nm or thereabouts.

I don't think most fluorescent light or LED sources pose a serious hazard. People have been working under fluorescent lights for close to one hundred years. Arc lamps and short wave fluorescent tubes are another matter however.

When UV fluorescence observation is done for gemstones one can wear clear or amber (minus blue) tinted polycarbonate lenses as part of the test. This blocks UV from reaching the eye surface and causing tears to autofluoresce which can confuse the viewer.

"Reactolite" type photochromic spectacles are interesting.
Shining the torch from the front, they go dark immediately.
Shining from the eye side, they don't, at all.
It seems that the treatment is on the front, and the remainder of the plastic lens is UV opaque, so it doesn't reach the darkening layer from eye-side.

They apparently stop all UV.
The glowing led is very obvious to me, though the 420nm longpass, without my specs. With them, it vanishes._________________Chris R

There is a bit of individual variation in the UV transparency of the crystalline. Usually, it also gets yellower, and less transparent to UV, with age. If the crystalline is surgically removed and replaced with an artificial lens transparent to UV (there are/were such lenses), i.e. to treat cataract, the individual acquires some measure of "UV vision". The retina is indeed somewhat sensitive to the longest UVA wavelengths, and it might even fluoresce in the VIS if exposed to UV, thus working like a downconverting imager.

These LEDs have a rather long emission "tail". It is normal to see some VIS violet emitted by them, and this is why some photographers prefer to mount a U340 on the head of the flashlight (U360 transmits a bit too much violet and does not completely bock the VIS emission.

Having said that, without quantitative measurements we cannot be sure that the LED is actually emitting at 365 nm and not a longer wavelength. The same Nichia LED model is available in sorting "bins" with different peak wavelengths, down to 405 nm, and these longer-wavelength bins are sold at lower prices. We don't know yet what the manufacturer actually used._________________--ES

I wonder how hard it would be to set up a diffraction grating and small diode, or webcam with filter removed, to get an idea of the spectrum.

It is possible in theory, but in practice it is difficult to get a sufficiently wide physical breadth of the spectrum to get a precision of 5 nm or so. It requires at least a slit aperture and a focusing mirror, in addition to a diffraction grating.

Then you need a calibration source, like a mercury lamp. However, I tested "UV" fluorescent lamps for enamel hardening with a spectrometer, and saw an almost nonexistent 365 nm mercury line (in addition to plenty of phosphor emission in the VIS), so this type of lamp is useless for calibration. I am sure that UVC fluorescent lamps for water sterilization emit a strong enough 365 nm line, but these lamps are best left alone because they also emit plenty of highly dangerous UVC and UVB (unless one can filter out the UVC in a reliable way, like a light-tight enclosure of sunbed-grade acrylic that transmits UVA).

In one of my earlier posts you can see an uncalibrated spectrum of an MTE 301 UV flashlight, rated at 365 nm (but these Nichia LEDs, even in the 365 nm bin, are only rated at +/-4 nm). Once I get the equipment I ordered, I will publish also a spectrum of the Convoy S2+, here or on my web site._________________--ES